| Background: Currently, bracing and surgical treatment were commonly used dealing with spinal deformity. However, there are still some severe problems and complications because of controlling or correcting deformity in use of external strength. From the point of physiology, bracing is rational, which could preserve the structure and function of spine. But, for the reason of indirect force, the therapeutic efficacy was not ideal in many cases, and some cases are not suitable to be treated with bracing. Surgical treatment has achieved great advancements in correcting, but it is no choice to patients, when getting beautiful shapes, they have been deprived of partial functions and had rigid spines.During the growth of spine, multiple organic centers are formed. It is possible to control certain organic centers in modulating spinal growth. At the same time, spinal deformity is to be corrected and partial functions be retained. With more investigations of spinal deformity and further developments in minimally invasive surgery of spine, it may be available to control or correct spinal deformity through spinal growth control.Objective: For the development and clinical application of native medical equipments, 3 tests were made. Design shape memory alloy (SMA) staples by means of shape memory effect and anti-fatigue of Nitinol alloys, evaluate it through biomechanical test, observe the process of controlled spine after implanting staples and histomorphological changes of vertebrae and intervertebral discs in the fixed segments.Methods: 1.Six fresh specimens of the vertebrae(T6~T11) in goats(age 2~3 months) were used to detect the vertical distance between one third of superior and inferior planes of two adjacent vertebrae, and maximum, intermedial transverse diameter and sagittal diameter in one third of superior and inferiorplanes of each vertebrae. According to these measurements, SMA staples of 5, 6.5 and 8mm were designed. 2. To evaluate the biomechanical character of SMA staples: ? Twenty four SMA staples were divided into three groups: 5mm group, 6.5mm group, 8mm group. Each group had eight staples and the recovery stress was respectively measured. ?Four fresh specimens of the vertebrae(T6~Tll) in goats(age 2~3 months) were used and each was cut into three functional spinal units (FSU) of T6~T7,T8~T9 and T10~Tll.Then SMA staples and stainless steel staples were randomly implanted into FSUs, which were divided into four groups: 5mm group, 6.5mm group, 8mm group and stainless steel staples group. Pullout strength of staples in each FSU was measured. There were totally bilateral eight staples of four different FSUs in each group of SMA staples, as compared with twenty four staples in total in the group of stainless steel. ?Each of four fresh specimens of the vertebrae(T6~Tll) in goats(age 2~3 months) was divided into three conditions: normal, single staple, double staples. Under each condition, the angle and torque of spinal movements in left and right bending, left and right rotation, flextion and extention were tested. 3. SMA staples were implanted into right sides of T6~T11 vertebrae in eight normal goats(age 2~3 months, weight 6-1 Okg). Then deformity of thoracic vertebrae in goats were observed with X-ray in serial four months. All goats were sacrificed after four months and the histological changes of vertebral bodies and discs in fixed sections were observed.Results: 1. SMA staples were designed into two kinds: two-prone staples and four-prone ones. The distances between prone were respectively 5mm > 6.5mm and 8mm 2. ?The maximum recovery stresses of SMA staples in 5mm group, 6.5mm group, 8mm group were 138.73±12.05N , 119.65±16.34N, 96.95±18.27N. The differences between groups were statistically significant (P<0.05).(2)The maximum pullout strength in 5mm group, 6.5mm group, 8mm group and stainless steel group were 74.18±8.81N, 51.28±5.44N, 39.13±7.54N, 20.62±9.15N. The differences between groups were statistically significant (P<0.05). (3)In left andright bending, flextion, extention, the stability of spine were decreased in conditions of single staple and two staples compared to normal condition(P<0.05). And in left and right rotation, there was no significant difference between those two conditions and normal one (P>0.05). 3. Of the eight goats, seven developed scoliosis and two kyphosis. Of sixty SMA staples implanted, there were only five loosening. The stabilities of spine in fixed segments were increased after 4 months. Wedge vertebrae appeared on the concave of T8. Histologic sections of vertebrae revealed a consistent fibrous tissue around SMA staple. In fixed segments, the height of epiphyseal and disc in concave vertebrae was lower than in convex side. Abnormal morphology and disarrangement of Epiphyseal cartilage cells were observed.Conclusions: 1 .Biomechanical function of SMA staples was superior to stainless steel staple. 2.1n vitro, instant stability of spine was decreased and increased after implanting staples in vivo for certain times. At the same time, partial functions were also reserved in the fixed segments. 3. SMA staples have the function hemiepiphysiodesis compression and kyphosis and scoliosis model of thoracic vertebrae in goat could be successfully created by the fusionless technique.
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